In recent years, a cab structure is employed which is composed of pipe members with a cavity inside as pole members of a cab that is installed on a construction machine.
This type of cab structure that is installed on a construction machine is required to satisfy safety standards of Excavator's Operator Protection Structure (EOPS). Accordingly, pipes that are used as the pole members are also required to satisfy a predetermined value in strength. However, if the thickness of pipe is increased to improve the strength, material cost and processing cost will increase. This results in high cost. For this reason, there is a need for a reinforcement structure for a pipe that can solve problems of both strength and cost.
For example, Japanese Patent Laid-Open Publication TOKUKAI No. 2006-240568 (published on Sep. 14, 2006) discloses a structure that, in order to reinforce a pillar (pole member) that is composed of bonded sheet metal members, has a plate member that is arranged from the top end to the bottom end inside the pillar.
In addition, Japanese Patent Laid-Open Publication TOKUKAI No. 2005-111557 (published on Apr. 28, 2005) discloses a double-pipe arrangement tube production method that includes a diameter reduction process for reducing the external peripheral length of an outer pipe after an inner pipe is inserted into the outer pipe whereby forming a double-pipe arrangement tube to reinforce the pipes.